two linked *monosaccharide molecules. For example, sucrose comprises one glucose molecule and one
fructose molecule bonded together.
discharge 1. The conversion of the
chemical energy stored in a *secondary cell into electrical energy.
2. The release of electric charge from
a capacitor in an external circuit.
3. The passage of charge carriers
through a gas at low pressure in a
discharge tube. A potential difference
applied between cathode and anode
creates an electric Üeld that accelerates any free electrons and ions to
their appropriate electrodes. Collisions between electrons and gas molecules create more ions. Collisions
also produce excited ions and molecules (see excitation), which decay
with emission of light in certain
parts of the tube.
disconnection See retrosynthetic
analysis.
disilane See silane.
dislocation See crystal defect.
disodium hydrogenphosphate(V) (disodium orthophosphate) A colourless crystalline solid,
Na 2 HPO 4 , soluble in water and insoluble in ethanol. It is known as the dihydrate (r.d. 2.066), heptahydrate
(r.d. 1.68), and dodecahydrate (r.d.
1.52). It may be prepared by titrating
phosphoric acid with sodium hydroxide to an alkaline end point (phenolphthalein) and is used in treating
boiler feed water and in the textile
industry.
disodium orthophosphate See
disodium hydrogenphosphate(v).
disodium tetraborate-10-water
See borax.
d-isomer See optical activity.
d-isomer See absolute configuration.
disordered solid A material that
neither has the structure of a perfect
*crystal lattice nor of a crystal lattice
with isolated *crystal defects. In a
random alloy, one type of disordered
solid, the order of the different types
of atom occurs at random. Another
type of disordered solid is formed by
introducing a high concentration of
defects, with the defects distributed
randomly throughout the solid. In an
*amorphous solid, such as glass,
there is a random network of atoms
with no lattice.
disperse dye See dyes.
disperse phase See colloids.
dispersion forces See van der
waals’ force.
displacement reaction See substitution reaction.
disproportionation A type of
chemical reaction in which the same
compound is simultaneously reduced
and oxidized. For example, copper(I)
chloride disproportionates thus:
2CuCl → Cu + CuCl 2
The reaction involves oxidation of
one molecule
Cu
I
→ Cu
II + e
and reduction of the other
Cu
I + e → Cu
The reaction of halogens with hydroxide ions is another example of a
disproportionation reaction, for example
Cl 2 (g) + 2OH
– (aq) ˆ Cl
– (aq) +
ClO
– (aq) + H 2 O(l)
The reverse process is *comproportionation.
dissipative system A system that
involves *irreversible processes. All
real systems are dissipative (in contrast to such idealized systems as the
frictionless pendulum, which is invariant under time reversal). In a dis181
dissipative system
d
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fructose molecule bonded together.
discharge 1. The conversion of the
chemical energy stored in a *secondary cell into electrical energy.
2. The release of electric charge from
a capacitor in an external circuit.
3. The passage of charge carriers
through a gas at low pressure in a
discharge tube. A potential difference
applied between cathode and anode
creates an electric Üeld that accelerates any free electrons and ions to
their appropriate electrodes. Collisions between electrons and gas molecules create more ions. Collisions
also produce excited ions and molecules (see excitation), which decay
with emission of light in certain
parts of the tube.
disconnection See retrosynthetic
analysis.
disilane See silane.
dislocation See crystal defect.
disodium hydrogenphosphate(V) (disodium orthophosphate) A colourless crystalline solid,
Na 2 HPO 4 , soluble in water and insoluble in ethanol. It is known as the dihydrate (r.d. 2.066), heptahydrate
(r.d. 1.68), and dodecahydrate (r.d.
1.52). It may be prepared by titrating
phosphoric acid with sodium hydroxide to an alkaline end point (phenolphthalein) and is used in treating
boiler feed water and in the textile
industry.
disodium orthophosphate See
disodium hydrogenphosphate(v).
disodium tetraborate-10-water
See borax.
d-isomer See optical activity.
d-isomer See absolute configuration.
disordered solid A material that
neither has the structure of a perfect
*crystal lattice nor of a crystal lattice
with isolated *crystal defects. In a
random alloy, one type of disordered
solid, the order of the different types
of atom occurs at random. Another
type of disordered solid is formed by
introducing a high concentration of
defects, with the defects distributed
randomly throughout the solid. In an
*amorphous solid, such as glass,
there is a random network of atoms
with no lattice.
disperse dye See dyes.
disperse phase See colloids.
dispersion forces See van der
waals’ force.
displacement reaction See substitution reaction.
disproportionation A type of
chemical reaction in which the same
compound is simultaneously reduced
and oxidized. For example, copper(I)
chloride disproportionates thus:
2CuCl → Cu + CuCl 2
The reaction involves oxidation of
one molecule
Cu
I
→ Cu
II + e
and reduction of the other
Cu
I + e → Cu
The reaction of halogens with hydroxide ions is another example of a
disproportionation reaction, for example
Cl 2 (g) + 2OH
– (aq) ˆ Cl
– (aq) +
ClO
– (aq) + H 2 O(l)
The reverse process is *comproportionation.
dissipative system A system that
involves *irreversible processes. All
real systems are dissipative (in contrast to such idealized systems as the
frictionless pendulum, which is invariant under time reversal). In a dis181
dissipative system
d
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